INFICON T-Guard Leak Detection Sensor - Manual (Page 46)

44
Operation
jina
85
e 5
.fm
Tech
ni
ca
l Ha
nd
bo
ok
(1
11
2)
Accumulation Measurement
In Accumulation mode, the T-Guard™ Leak Detection Sensor starts with the G ROSS
leak test. If, at the beginning of the test, the helium concentration in the chamber is
much higher (approx. 1000 ppm) than in the environment, the test sample has a
gross leak.
In this case, the T-Guard™ stops the measurement cycle and displays a leak rate of
a hundred times the highest trigger value.
If the test sample passes the GROSS -leak test, the T-Guard™ Leak Detection
Sensor takes an air sample from the chamber and measures it in F
INE -mode.
If, during this first FINE measurement, the T-Guard™ detects that the helium concen-
tration rises too fast, it will stop the measurement and report a leakage rate of five
times the highest trigger level.
After the first FINE -measurement, it will wait for a certain time. Then, the second
GROSS measurement will be carried out to check if the test sample has exploded.
After that, it takes the next air sample in FINE-mode. From the difference of the two
F
INE -measurements, the T-Guard™ Leak Detection Sensor calculates the leak rate.
Fig. 6-7 Typical helium concentration in an enclosed chamber with a leaky test
sample over time. Due to ambient helium, the helium level is never zero.
The helium level rises linearly with time. The T-Guard™ Leak Detection
Sensor measures the helium concentration in the chamber four times.
Item Description Item Description
1 Helium concentration 7 Accumulation time
2 Start 8 Second gross measurement
3 Ambient helium 9 Second fine measurement
4 Time 10 Wait time purge
5 First gross measurement 11 Purge time
6 First fine measurement 12 Measuring time